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A141220
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Nonprimes of the form ((p(max)+2)*..*p*(p(min)-1)), where a(0)=1 and (p(max))*..*p*(p(min)=k(n)=n-th nonprime.
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4
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1, 4, 8, 10, 10, 9, 14, 16, 15, 14, 18, 20, 28, 15, 30, 18, 21, 32, 26, 36, 30, 21, 30, 28, 27, 26, 42, 25, 40, 54, 35, 38, 30, 45, 52, 36, 42, 42, 33, 54, 64, 60, 39, 38, 50, 45, 60, 39, 70, 42, 78, 45, 56, 90, 54, 76, 45, 62, 52, 63, 90, 50, 66, 49, 84, 80, 63, 78, 70, 57, 60
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| If k(1)=4=(p(max)=2)*(p(min)=2), then (2+2)*(2-1)=4*1=4
(nonprime)=a(1).
If k(2)=6=(p(max)=3)*(p(min)=2), then
(3+2)*(2-1)=5*1=5 (prime).
If k(3)=8=(p(max)=2)*(p=2)*(p(min)=2), then
(2+2)*2*(2-1)=4*2*1=8 (nonprime)=a(2), etc.
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MAPLE
| Contribution from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Mar 29 2010: (Start)
A006530 := proc(n) if n = 1 then 1; else max(op(numtheory[factorset](n))) ; end if; end proc:
A020639 := proc(n) if n = 1 then 1; else min(op(numtheory[factorset](n))) ; end if; end proc:
A002808 := proc(n) if n = 1 then 4; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do; end if; end proc:
A052369 := proc(n) A006530(A002808(n)) ; end proc: A056608 := proc(n) A020639(A002808(n)) ; end proc:
A141220 := proc(n) if n = 0 then 1; else c := A002808(n) ; hi := A052369(n) ; lo := A056608(n) ; c*(hi+2)*(lo-1)/lo/hi ; end if; end proc:
printf("1, ") ; for n from 1 to 400 do a := A141220(n) ; if not isprime(a) then printf("%d, ", a) ; end if; end do: (End)
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CROSSREFS
| Sequence in context: A072037 A084093 A076703 * A108806 A074776 A153762
Adjacent sequences: A141217 A141218 A141219 * A141221 A141222 A141223
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KEYWORD
| nonn
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AUTHOR
| Juri-Stepan Gerasimov (2stepan(AT)rambler.ru) Aug 7 2008
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